[Tango Echo Dog]

John
The idea that there were 10,000 Americans in the RAF in 1940 is bull's hit.
Less than a dozen American pilots participated in the Battle of Britain and 244 served in the Eagle squadrons which began to appear at the very end of this battle.
In 1940 the RAF wanted pilots rather than ground-crew, pen-pushers etc and they could get these from the pre-war regulars augmented by the first conscripts. The RAF was obsessed with pilots who, in multi-engined aircraft, were expected to fly, navigate, command and watch out for Kryptonite.
Even with the limited statistical information above it is clear that in 1940 there were no more than 100 Americans in the RAF and that is probably pushing it, although in August 1918 a surprisingly high number of RAF aircrew were born under the Star Spangled Banner. Most Americans wanting to join up in World War Two would indeed join the RCAF but by Pearl Harbor there were only 6,700 Americans in that organisation.
Regards
Tango Echo Dog